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  • Blackwell Publishing Ltd  (7)
  • American Institute of Physics (AIP)  (2)
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  • Blackwell Publishing Ltd  (7)
  • American Institute of Physics (AIP)  (2)
  • Springer  (6)
  • Elsevier  (1)
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  • 1
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 88 (2000), S. 1407-1411 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The sublimation epitaxy growth process has been studied. The structural quality of the grown layers improves compared with the substrate mainly due to a diminished domain structure misorientation. Optical microscopy shows that the as-grown surfaces are free of typical defects appearing in silicon carbice (SiC) epitaxy, whereas atomic force microcopy measurements show macrosteps. As a possible technique to produce high-quality 4H–SiC, sublimation epitaxy was performed on substrates containing a layer grown by liquid phase epitaxy which is a growth process for closing micropipes in the initial substrate. In spite of the initial surface roughness of the liquid phase epitaxy layer, the surface morphology of the sublimation grown epilayers remained smooth and the structural quality improvement was maintained. This does not occur if the initial surfaces are too rough. A suggestion for roughness reduction is presented. The growth conditions (growth rate ramp up, growth temperature, temperature gradient, source to substrate distance, and substrate surface orientation) leading to the results are presented. A model for the mechanism for structural improvement is outlined and supporting experimental observations are given. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1365-3083
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: The mixed lymphocyte culture (MLC) response of lymphocytes from CBA mice against C3H cells was studied after injection of spleen cells from C3H mice or C3H hybrids. Intravenous infusion of C3H cells resulted in a strongly suppressed specific MLC response, but this was not the case when cells from H-2-incompatible hybrids of C3H mice were injected. However, when mixtures of cells from the two parental strains-C3H cells and H-2-incompatible cells-were injected into CBA mice, there was a strongly suppressed MLC response to C3H cells. Mice that were hybrids between CBA and an H-2-disparate strain showed a depressed MLC response against C3H after injection of cells from hybrids between C3H and the same H-2-disparate strain. The results may indicate that a suppression of the MLC response to the strongly stimulatory non-H-2 antigen on C3H lymphocytes develops only when the immunizing cells can survive in the host for long periods, thus exhausting the pool of specifically responsive cells. The presence of another foreign transplantation antigen, such as H-2, on the same cells shortens the survival of the cells in the recipient.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    ISSN: 1365-3083
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: Injection of CBA mice with H-2-compatible lymphoid cells from C3H hybrids induces a specific reduction of the mixed lymphocyte culture (MLC) response of their lymphoytes. This is not the case after injection of H-2-disparate C3H-hybrid cells, presumably because they are rapidly eliminated due to the immune response of the host. This investigation shows that CBA mice injected with CBA × C57B1 cells (H-2-disparate) at an age of 0–3 days, but not older, develop a specifically reduced MLC response after infusion of C3H × C57B1 cells as adults, indicating that they were tolerant to the C57B1-determined antigens. However, lymphocytes from such mice showed a normal reactivity against C57B1 as assessed by MLC, graft-versus-host tests, and capacity to produce specific antibodies.
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  • 4
    ISSN: 1365-3083
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: The capacity of lymphocytes from mouse strain CBA to generate ‘effector’ cells against the H-2-compatible, M-antigen-incompatible strain C3H and their interaction with such target cells were investigated. It was observed that CBA lymphocytes injected in, and 5 days later obtained from, the spleens of irradiated C3H × CBA hybrids (‘educated cells’) could strongly inhibit the growth of C3H × CBA bone marrow cells but were almost nonresponsive to C3H × C57BI bone marrow targets (H-2-incompatible). CBA lymphocytes educated in irradiated C3H × C57B1 hosts displayed reactivity against C3H × C57B1 and CBA × C57B1 but not against C3H × CBA bone marrow target cells. Additional tests indicated that the M antigen determined by C3H is expressed td approximately the same extent on C3H × CBA and C3H × C57B1 cells and that the M antigen on C3H does not cross-react immunologically with antigens on C57B1 cells. Moreover, it was observed that CBA × C57B1 lymphocytes were triggered to cell proliferation by C3H antigens but were unable or had a highly reduced capacity to develop ‘effector’ cells in response to this antigenic stimulus. These results indicate that generation of ‘effector’ cells and their interaction with target cells are very complex processes.
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  • 5
    ISSN: 1365-3083
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: Lymphocytes from mice of strain CBA are strongly MLC-responsive to lymphocytes from the H-2 compatible- but M-antigen-incompatible strain C3H. This strong reactivity disappears after infusion of CBA mice with C3H lymphocytes. This study shows that the host-versus-graft reactivity (swelling of local lymph node after antigen injection) is specifically reduced after injection of CBA mice with C3H × CBA spleen cells However, lymphocytes from such mice showed a specifically increased GVH reactivity (inhibition of erythroid cell growth) compared with lymphocytes from unimmunized mice. Lymphocytes from normal CBA mice showed a high proliferative rate in the spleens of irradiated C3H × CBA mice. Such ‘educated’ cells showed strongly increased specific GVH reactivity. Lymphocytes from CBA mice previously injected with C3H×CBA cells showed reduced capacity to proliferate when injected into irradiated C3H × CBA hybrids and a poor capacity to develop new ‘effector’ cells reactive against C3H × CBA bone marrow target cells. The results indicate that the presence of specifically ‘MLC responsive’ lymphocytes in a lymphoid cell population is a prerequisite of its production of ‘effector’ cells able to respond in this GVH assay
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  • 6
    ISSN: 1365-3083
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: The thymocyte population of mice treated with cortisone was examined at various times with respect to its relative capacity to be triggered to DNA synthesis by soluble phytomitogens or mitogenic factors (MF) released by lymph node cells exposed to phytomitogens. The capacity of the thymocyte population to produce MF in response to phytomitogen exposure was also examined. We found that the relative blastogenic activity of both phytomitogens and MF on thymocytes increased as the cell number of the thymus was reduced by the cortisone treatment. However, the reactivity to phytomitogens increased to a higher extent. During the subsequent regeneration of the organ the stimulability of the cells by phytomitogen decreased far below that of MF. The relative capacity of thymocytes to produce MF seemed to parallel their phytomitogen reactivities One possible explanation of the results is that there exists one subpopulation of cells in the thymus more responsive to phytomitogens than to MF and another more responsive to MF than to phytomitogen. It is possible that the cells that are phytomitogen-responsive are those that can produce MF.
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  • 7
    ISSN: 1365-3083
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: The mixed lymphocyte culture (MLC) response of lymphocytes from CBA mice injected with spleen cells from the H-2-compatible strain C3H was studied. The response of CBA lymphocytes against C3H cells was higher than that obtained against H-2-disparate strains Intravenous injection of C3H cells resulted in a markedly increased MLC response in lymph nodes but not in the thymus during the first 1 to 3 days Thereafter, the specific MLC response decreased drastically, far below that of nonimmunized animals. Reactivity was back to normal in the thymus after approximately 4 weeks but remained suppressed in lymph nodes for more than half a year. A decreased response was also noted in spleen, Peyer's patches, and the peripheral blood lymphocyte population Such a state of relative unresponsiveness was achieved by injecting as few as 104 C3H spleen cells. This exhaustion of the specific MLC response could not be explained by production of Mocking serum factors or of cells that can inhibit the MLC response. The strong MLC response obtained by lymphocytes from nonimmunized animals may be due to disparity at the newly detected M locus This antigenic system is characterized by strong MLC stimulatory capacity and no detectable production of humoral antibodies or development of effector cells capable of killing M antigen bearing cells A possible explanation of the results is that the CBA mice become chimaeric for a long time after injection of C3H cells. This prolonged exposure to a foreign transplantation antigen may lead to exhaustion of the specifically responsive lymphocytes.
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  • 8
    ISSN: 1365-3083
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: The thymocyte population of mice treated with cortisone was examined at various times with respect to its relative capacity to be triggered to DNA synthesis by soluble phytomitogens or mitogenic factors (MF) released by lymph node cells exposed to phytomitogens. The capacity of the thymocyte population to produce MF in response to phytomitogen exposure was also examined. We found that the relative blastogenic activity of both phytomitogens and MF on thymocytes increased as the cell number of the thymus was reduced by the cortisone treatment. However, the reactivity to phytomitogens increased to a higher extent. During the subsequent regeneration of the organ the stimulability of the cells by phytomitogen decreased far below that of MF. The relative capacity of thymocytes to produce MF seemed to parallel their phytomitogen reactivities Onepossible explanation of the results is that there exists one subpopulation of cells in the thymus more responsive to phytomitogens than to MF and another more responsive to MF than to phytomitogen. It is possible that the cells that are phytomitogen-responsive are those that can produce MF.
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  • 9
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The goal of this study is to investigate the effect of carbon incorporation upon thermal oxidation of Si1−xGex alloys and its role on strain compensation in Si1−xGex alloys. Si1−xGex and Si1−x−yGexCy alloys on Si(100) are grown by combined ion and molecular beam deposition and are then oxidized at 1000 °C in a dry oxygen ambient for two h. The thickness and the composition of all samples before and after oxidation are measured by Rutherford backscattering spectrometry (RBS) combined with ion channeling at 2.0 MeV and carbon nuclear resonance analysis at 4.3 MeV using 4He++ ions. In agreement with previously reported results of dry oxidation on Si1−xGex thin films, 2.0 MeV RBS analysis shows that a layer of SiO2 is formed on the top surface of both Si1−xGex and Si1−x−yGexCy thin films, while Ge segregates towards the top surface and at the SiO2/Si1−xGex and SiO2/Si1−x−yGexCy interfaces. However, it is observed for the first time that dry oxidation rates of Si1−xGex thin films decrease with increasing Ge fraction x for x(approximately-greater-than)0.20 and with increasing minimum yield. Ion channeling analysis and strain measurements indicate that the incorporation of C rather than the amount of C itself affects the dry oxidation mechanism because of its strong influence on film strain and crystalline quality. These results are discussed in conjunction with observations by secondary ion mass spectrometry, high resolution transmission electron microscopy, Fourier transform infrared spectrometry, and tapping mode atomic force microscopy. © 1996 American Institute of Physics.
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